Heat exchanger tube and corresponding heat exchanger

ABSTRACT

The strip of material (11) forming the tube (5) is folded on itself such as to define at least one fold (13) formed by two strip portions (13a, 13b) with continuity of material. At least one strip portion (13a, 13b) of the fold (13) is a strip portion (13a, 13b) for protecting the tube (5) in the event of an impact from an element outside the tube (5) and is formed in an intermediate part (11 b) of the strip of material (11).

The invention relates to a heat exchanger tube, notably for motorvehicles. The invention also relates to a heat exchanger comprising abundle of such tubes.

The invention pertains to the field of heat exchangers, notably formotor vehicles.

The present invention relates in particular to heat exchangers designedto be placed at the front end of a motor vehicle. A front end, alsocalled a front end assembly, is a structural element that is able toincorporate a variety of equipment of the vehicle, such as headlamps,flashers, audible warning device, heat exchangers, engine fans orcooling module.

The heat exchanger is, for example, used to cool the engine or, again,to air-condition the car interior.

Generally, heat exchangers conventionally comprise a bundle of tubes andcollector boxes into which the ends of the tubes of the bundle open outsuch as to allow the circulation of a fluid, notably a cooling fluid, inthe tubes of the bundle.

The tubes of such exchangers may be produced, for example, by extrusion.This type of manufacture gives rise to a significant cost, however,notably owing to the need for specific dies for each type of tube.

In a variant, tubes are produced from a strip of material, for example,by folding the strip of material.

However, the tubes of heat exchangers may be subject to numerousstresses, such as a high-speed impact with an object (for example, apiece of gravel) originating from the exterior environment. The tubes ofheat exchangers are thus subject to exterior stresses. The fluid mustnot escape from the tubes of heat exchangers as this is likely tocompromise the way in which these heat exchangers function, so it isnecessary to preserve the exterior/fluid leaktightness of the tubes.

With a view to protecting these heat exchangers, a grille, generally onemade from plastics, may be incorporated at the front end in order tostop pieces of gravel. Nevertheless, the integration of such a grille atthe front end engenders a certain cost.

It has proven to be useful to guarantee that the material used for thetube is sufficiently strong in order to prevent any risk of fluidescaping from the heat exchanger, for example in the event of an impactwith a piece of gravel on the road.

A known solution is to enable the tube to withstand such an impact bylocally increasing the thickness of the wall of the tube in the case ofan extruded tube. However, such tubes are expensive to manufacture.Moreover, it has been observed that such tubes are lesscorrosion-resistant than tubes made from a strip of material, notably byfolding.

In a first known tube produced from a strip of material, the end partsof the tube are folded and secured together by brazing, on a side or atthe tube nose. Such folds that are brazed at the end parts require acomplex manufacturing process.

Furthermore, such tubes may not be sufficiently able to withstand impactfrom pieces of gravel.

Thus, an object of the invention is to propose a solution for a tubeproduced from a strip of material, conferring, on the tube, in a simplemanner, improved resistance to exterior stresses while still resolvingthe above-mentioned prior-art drawbacks at least in part.

To that end, a subject of the invention is a tube for a heat exchangermade from a strip of material, the strip of material having two endparts joined such as to form the tube. According to the invention, thestrip of material forming the tube is folded on itself such as to defineat least one fold formed by two strip portions with continuity ofmaterial such that at least one strip portion of the fold:

-   -   is a strip portion for protecting the tube in the event of an        impact from an element outside the tube, and    -   is formed in an intermediate part of the strip of material.

The two strip portions of said at least one fold may be formed in theintermediate part of the strip of material.

In other words, the intermediate part of the strip of material is bydefinition distinct from, i.e. does not include, the lateral ends of thestrip of material.

The end parts of the strip of material each include a lateral end of thestrip of material.

It is possible, for example, to define the intermediate part of thestrip of material as the central part corresponding to 80% of the widthof the strip of material, the end parts corresponding, for example, tothe parts having a width of 10% on either side of the intermediate part.

However, this value of 80% is purely indicative. The important thing isfor the intermediate part not to include the lateral ends of the stripof material.

Furthermore, the intermediate part has a longitudinal extensioncorresponding to the longitudinal extension of the tube.

Thus, advantageously in locations where there are high levels of stress,notably stresses from outside the tube, this fold or these folds areused to create one or more zones of reinforcement of the tube that makeit possible to absorb energy in the event of an impact from an elementoriginating from the exterior environment, such as a piece of gravel.

The one or more folds are not produced in a zone where walls of thestrip of material that need to be leaktight join or overlap, but thewall is folded on itself with continuity of material. Thus, even werethe folds to deform or to unfold, the leaktightness of the tube,furthermore achieved, for example, by brazing or electrowelding, wouldremain guaranteed.

The invention thus offers the advantage of protection for the joinbetween the end parts of the strip of material and thus theleaktightness of the tube.

Said tube may, furthermore, comprise one or more of the followingfeatures, taken separately or in combination.

Preferably, the intermediate part does not include a join zone betweenthe two end parts in order to close the tube in a sealed manner. Inother words, the intermediate part lacks such a join zone.

According to one aspect of the invention, said at least one fold isformed along at least one lateral side of the tube. This side isconfigured such as to be arranged on the front side of a heat exchangerfacing an inlet for a flow of external air at the front end of a motorvehicle.

According to one example, the tube has two major sides connected by twolateral minor sides. Said at least one fold is formed on a lateral minorside.

According to another aspect of the invention, the strip portions of saidat least one fold are brazed together such as to increase the mechanicalstrength of the tube.

The strip portions of said at least one fold may or may not lie againstone another.

According to a first embodiment, the strip of material is folded such asto form a protuberance extending from the tube toward the exterior ofthe tube.

Such a protuberance is the first surface of the tube with which a pieceof gravel, for example, enters into contact in the event of impact. Theprotuberance may fold and/or deform through the effect of the impact andthus absorb the energy of the piece of gravel.

Lastly, such a tube may be produced in a simple manner without requiringa plurality of manufacturing steps.

The protuberance may have a thickness at least equal to twice thematerial thickness of the strip of material.

For example, the protuberance forms, with the horizontal, a non-zeroangle notably less than or of the order of 45°, preferably of the orderof 30°.

The protuberance may extend over a width equal to at least twice and toat most ten times the material thickness of the strip of material.

According to a second embodiment, the strip of material is folded in thedirection of the height of the tube, such as to form an excess thicknessof material.

A sufficient excess thickness, advantageously provided at the nose ofthe tube, is obtained with a view to guaranteeing mechanical strengthand thereby protecting the tube in the event of impacts originating fromthe exterior environment, without the risk of a leak of fluid.

The height of the strip portions of said at least one fold is, forexample, of the order of the height of the tube.

According to either embodiment, the tube is a folded tube. The tube mayhave a cross section substantially in the form of a “B”, defining twoparallel fluid-circulation channels delimited by a separation.

The tube may be an electrowelded tube.

The invention further relates to a heat exchanger, notably for a motorvehicle, characterized in that it comprises a bundle of tubes as definedabove.

Further features and advantages of the invention will become moreclearly apparent upon reading the following description, given by way ofillustrative, non-limiting example, and the appended drawings, in which:

FIG. 1 shows, in part and schematically, a heat exchanger,

FIG. 2 is a cross-sectional view showing, in part, a first example of atube of the exchanger of FIG. 1,

FIG. 3 is a cross-sectional view of a second example of a tube of theexchanger of FIG. 1,

FIG. 4 is a cross-sectional view of a third example of a tube of theexchanger of FIG. 1, and

FIG. 5 is a cross-sectional view of a fourth example of a tube of theexchanger of FIG. 1.

In these figures, identical elements bear the same references.

The following embodiments are examples. Although the description relatesto one or more embodiments this does not mean necessarily that eachreference relates to the same embodiment or that the features apply toonly one embodiment. Simple features from different embodiments maylikewise be combined or interchanged in order to provide furtherembodiments.

In the description, certain elements may include an index mark such as,for example, first element or second element. In this event, this issimple indexing to differentiate and to name similar but not identicalelements. This indexing does not imply that any element takes priorityover any other element, and such designations may easily be interchangedwithout departing from the scope of the present description. Thisindexing does not, likewise, imply an order in terms of time.

FIG. 1 schematically shows an example of a heat exchanger 1 according tothe invention. This is, in particular, a heat exchanger 1 designed to beplaced at the front end of a motor vehicle.

An example that may be cited is that of radiators for cooling the engineor, again, “low-temperature” radiators, for example for auxiliarycooling circuits in the motor vehicle. It may also be, for example, acondenser of an air-conditioning circuit.

The heat exchanger 1, such as a cooling radiator, placed at the frontend of the vehicle may be accessed by a first fluid, such as a flow ofexternal air, originating from outside the vehicle. A second fluid, suchas a cooling fluid, circulates inside the heat exchanger 1 such as toexchange heat with this flow of external air.

The heat exchanger 1 has a front side A, i.e. designed to be arranged onthe side of the grille of the motor vehicle or, alternatively, facing aninlet for the flow of external air designed to traverse the heatexchanger 1. The heat exchanger 1 also has a rear side B, or engineside, which is opposite the front side A.

In the present description, the terms front/rear are designed to referto the direction of progress, in a forward gear, of the motor vehicleintended to be equipped with a heat exchanger 1 as described. Similarly,the terms vertical/horizontal are designed to refer to the arrangementof the elements in FIGS. 2 to 5, which corresponds to the arrangement ofthe elements in the assembled state in the motor vehicle.

As illustrated in part in FIG. 1, the heat exchanger 1 conventionallycomprises a bundle 3 (shown very schematically in FIG. 1) of tubes 5.

Examples of tubes 5 are in part shown in FIGS. 2 to 5. These tubes 5 aremounted between two distribution housings or collector boxes 7, alsocalled water boxes, (referring, likewise, to FIG. 1) for the secondfluid.

In the assembled state in the motor vehicle, the heat exchanger 1 may bearranged such as to allow, for example, a transverse circulation offluid in the tubes 5 that extend transversely to the motor vehicle.There are, however, configurations in which circulation takes placevertically in vertical tubes 5.

Advantageously, the heat exchanger 1 is a “brazed” exchanger. In thiscase, the various component parts of the body of such a heat exchanger 1are made from metal and may be assembled and then brazed by passingthrough a brazing furnace with a view to securing together all thecomponent parts. It should be noted that other elements made fromplastics, in particular, are typically attached on top after brazing,such as, for example, water boxes.

The tubes 5 (FIGS. 2 to 5) may extend longitudinally along a length L₅shown schematically in FIG. 1. The ends of these tubes 5 open out intothe collector boxes 7, for example by means of collector plates (notshown), which may be arranged transversely relative to the tubes 5.

Each tube 5 delimits one or more circulation channels 9 (see FIGS. 2 to5) for the second fluid.

The tubes 5 may be separated from one another by inserts (not shown),for example corrugated inserts, traversed by the first fluid, such asthe flow of external air, for the purposes of a thermal exchange withthe second fluid, such as the cooling fluid circulating in the tubes 5.

According to a variant embodiment (not shown), an internal insert, forexample a corrugated insert, may be inserted in the or each circulationchannel 9. This internal insert has, for example, a thickness of theorder of 80 μm to 140 μm.

The invention relates more precisely to a tube 5 for such a heatexchanger 1, examples of which are shown schematically in FIGS. 2 to 5.

The tube 5 is produced from a strip of material 11. This is, inparticular, a metallic strip 11. The metallic strip is preferably madeof aluminum or aluminum alloy. The strip of material 11 is, for example,of rectangular general shape.

This strip of material 11 has a thickness e, which, below, is alsocalled material thickness. This material thickness e is constant. By wayof example, the material thickness e may be of the order of 180 μm to270 μm, in particular of the order of 200 μm to 270 μm.

Notably, the tube 5 may be obtained from a reel of metallic foil that,after being unwound as a strip, is progressively formed to the requiredcross section using specific tools, for example folding or similartools, and is then cut to the desired length, in sections correspondingto a plurality of final tubes 5.

In particular, the strip of material 11 has end parts 11 a, which may beseen in the example of FIG. 4, which are joined such as to form the tube5, notably to close the tube 5 in a leaktight manner. These end parts 11a comprise the lateral ends or lateral borders of the strip of material11.

Leaktightness may be assured by brazing at the join of the end parts 11a. In a variant, this may be an electrowelded tube 5.

The strip of material 11 also has an intermediate part 11 b. Thisintermediate part 11 b does not include the lateral ends of the strip ofmaterial 11. The intermediate part 11 b is distinct from the end parts11 a.

By way of non-limiting example, the end parts 11 a of the strip ofmaterial 11 may extend on each side of the strip of material 11, eachover a width of the order of 10% of the total width of the strip ofmaterial 11.

The intermediate part 11 b, meanwhile, forms a central part extending,for example, over a width of the order of 80% of the total width of thestrip of material 11.

Furthermore, the end parts 11 a and the intermediate part 11 b each havea longitudinal extension corresponding to the longitudinal extension ofthe tube 5.

The tube 5 may be folded or formed such as to define a single channel 9for circulation of fluid (FIG. 3). By way of non-limiting example, thetube 5 may have a cross section of oblong general shape. The strip ofmaterial 11 then forms an envelope of this circulation channel 9.

In a variant, the tube 5 may be folded or formed such as to define atleast two circulation channels 9 (FIG. 4). The tube 5 may have a crosssection of “B” form.

The cross section of “B” form of the illustrated tube 5 has twojuxtaposed parallel channels 9 for circulation of fluid which areseparated by a separation forming a spacer. To that end, the metallicstrip is folded such as to form the envelope of these juxtaposedparallel circulation channels 9. The separation is produced jointly bythe folded opposite end parts 11 a of the strip of material 11. In thisexample, the intermediate part 11 b of the strip of material 11 does notinclude the join zone Z, which is encircled in a broken line in FIG. 4,of the two end parts 11 a to form the separation.

A description has been given here of a folded tube of “B” form.Naturally, provision may be made for any other type of folding.

The end parts 11 a of the strip of material 11, visible only in theexample of FIG. 4, may be placed against or superposed on one another.In particular, in the example of FIG. 4, the end parts 11 a may befolded up, for example substantially at a right angle, and placedagainst one another.

According to any of the variants shown in FIGS. 2 to 5, the tube 5 hastwo major sides 5 a, notably with a planar surface, connected by twolateral minor sides 5 b of height h, which defines the height h of thetube 5. These minor sides 5 b may be rounded and are likewise calledradii of the tube 5.

The height h of the tube 5 also corresponds to the overall thickness ofthe tube 5. This height h of a tube 5 is, for example, of the order of1.2 mm to 3 mm.

Moreover, during the method for manufacturing the tube 5, the strip ofmaterial 11 forming the tube 5 is folded on itself such as to define,with continuity of material, at least one fold 13.

This strip of material 11 is folded on itself at least at one side ofthe tube 5, also called the nose of the tube 5. This is a lateral minorside 5 b of the tube 5 intended to be arranged on the front side A ofthe heat exchanger 1. The side 5 b of the tube 5 having one or morefolds 13 is configured such as to extend along a transverse axis, in thedirection of the width, of a motor vehicle equipped with a heatexchanger 1 comprising such a tube 5.

Furthermore, the or each fold 13 is formed by two strip portions 13 a,13 b, with continuity of material, via a return 13 c. “With continuityof material” is understood to mean the fact that the fold 13 is notformed by two distinct walls secured together.

Each fold 13 thus forms a double thickness of strip. Only one fold 13 isshown in the examples of FIGS. 2 to 4. In the example of FIG. 5, twofolds 13 are shown and share a common strip portion 13 b. Naturally, theinvention is not limited to one or two folds 13.

Moreover, at least one of the strip portions 13 a or 13 b of the fold 13is a protective strip portion, i.e. it protects the tube 5 particularlyin the event of impact between an element from the exterior environmentand the tube 5.

At least the protective strip portion 13 a and/or 13 b of the fold 13 isformed along the nose or side 5 b of the tube 5.

At least the protective strip portion 13 a and/or 13 b is produced in anintermediate part 11 b of the strip of material 11. The two stripportions 13 a and 13 b forming a fold 13 may be produced in thisintermediate part 11 b of the strip of material 11. As statedpreviously, the intermediate part 11 b of the strip of material 11 doesnot include the lateral ends of the strip of material 11 and likewisedoes not include a join zone Z of the end parts 11 a (see FIG. 4) forjoining the strip of material 11. The protective fold 13 is thus notproduced at the end parts 11 a or, more precisely, at the lateral ends.

The strip portions 13 a, 13 b of each fold 13 may optionally be placedagainst one another.

Provision may be made for these strip portions 13 a, 13 b to be brazedtogether at each fold 13 such as to increase the mechanical strength ofthe tube 5. The fold or folds 13 being formed with continuity ofmaterial, such a brazing step does not have the effect of making thetube 5 leaktight.

First Solution

According to a first solution, different examples of which areillustrated schematically in FIGS. 2 to 4, the strip of material 11 isfolded such as to form a protuberance 15 or spur. This protuberance 15extends from the tube 5, more precisely from the side or nose of thetube 5, toward the exterior of the tube 5. In other words, thisprotuberance 15 extends away from the channel 9 for circulation ofcoolant fluid delimited by the tube 5.

In other words, the protuberance 15 is formed by the strip portions 13a, 13 b of the one or more folds 13. In this case, the strip portions 13a, 13 b of each fold 13 may be placed against one another and areadvantageously brazed together. Naturally, provision may be made formore than one fold 13.

This protuberance 15 formed from at least two strip portions 13 a, 13 bof a fold 13 thus has a thickness E equal to at least twice the materialthickness e of the strip of material 11 forming the tube 5.

Moreover, the protuberance 15 may extend over a width L₁₅ (referenced inFIG. 2), which is advantageously between twice and ten times thematerial thickness e of the strip of material 11 forming the tube 5.

Furthermore, the orientation of the one or more folds 13 forming theprotuberance 15 may be adapted in accordance with requirements, asillustrated in the examples of FIGS. 2 to 4.

Reference is now made to FIG. 2, which shows a sectional view of such atube 5 according to a first example. In this first example, the fold 13is formed horizontally in the figure. In this case, the protuberance 15,and thus the strip portions 13 a, 13 b forming it, extend parallel tothe major sides 5 a of the tube 5. This protuberance 15 extends in thetransverse direction of the tube 5.

The strip of material 11 forming the tube 5 is thus folded over one ormore times on itself horizontally (in the figure) at least at thelateral minor side 5 b or nose of the tube 5, thereby increasing thedimension of the tube 5 in the direction of the width or the transversedirection of the tube 5.

In this first example, the two strip portions 13 a and 13 b of the fold13 forming the protuberance 15 carry out the function of providingprotection in the event of impact by an exterior element, such as apiece of gravel.

In the first example of FIG. 2, the tube 5 is shown only in part, and ofcourse the cross section of this tube 5 may be oblong or, for example,of “B” form, as described previously.

In an alternative, the protuberance 15 may, with the general plane ofextension of the tube 5, corresponding in the figures to a horizontalplane, form a non-zero angle α. Such an alternative is illustrated in asecond example of a tube 5 in FIG. 3 and in a third example of a tube 5in FIG. 4. In other words, the protuberance 15 may form a non-zero angleα with the major faces 5 a of the tube 5.

In particular, the angle α may be of the order of or less than 45°.According to a particular example, the angle α is of the order of 30°.

The third example, of FIG. 4, differs from the second example, of FIG.3, in terms of the cross section of the tube 5 of “B” form instead ofthe oblong cross section.

In these examples, at least the first strip portion 13 a forming thefold 13, which is the outermost relative to the tube 5, is designed tobe the first surface in contact with an exterior element in an impact onthe tube 5 and performs at least the function of protection.

Second Solution

According to a second solution, illustrated schematically in FIG. 5, thestrip of material 11 is folded in the direction of the height h of thetube 5. Only differences from the examples of the first solution aredescribed below.

According to this second solution, the tube 5 thus has one or morevertical folds 13 that form an excess thickness E′ of material at leastat the nose of the tube 5 or lateral minor side 5 b. The vertical folds13 of the second solution are akin to the folds 13 according to thesecond and third examples of the first solution, forming a protuberance15 inclined at an angle of the order of 90° to the horizontal.

The tube 5 thus formed therefore has a variable thickness. In otherwords, the tube 5 has one or more reinforced zones, i.e. zones with agreater thickness which are obtained by folding the strip of material 11on itself. These reinforced zones correspond to the zones of the tube 5that are the most stressed, particularly the nose of the tube 5.

In a manner similar to the first solution, at least one of the stripportions 13 a, 13 b of the folds 13 forming the excess thickness E′performs the function of protecting the tube 5 in the event of impact byan exterior element such as a piece of gravel. Indeed, this excessthickness E′ also makes it possible to absorb the energy of the piece ofgravel in the event of impact.

In the example illustrated in FIG. 5, only two folds 13 with a commonstrip portion 13 b are shown. Naturally, there is no limitation on thenumber of folds 13. Provision may be made for a plurality of folds 13,in particular with an odd total number of strip portions 13 a, 13 b.

Furthermore, the folds 13 are produced over the entire height h of thetube 5. At the very least, the strip portions 13 a, 13 b of the folds 13must extend over a height corresponding to the height of the circulationchannel 9, i.e. the height h of a tube 5 minus twice the materialthickness e.

Thus, in the course of the method for obtaining such a tube 5, the stripof material 11 may be folded at at least an intermediate part 11 b, asdescribed according to any of the variants with reference to FIGS. 2 to5, such as to form, with continuity of material, at least one fold 13formed by two strip portions 13 a, 13 b, at least one strip portion 13 aand/or 13 b of which forms the protection for the tube 5.

This folding-over at at least an intermediate part 11 b of the strip ofmaterial 11 may take place prior to the folding of the strip of material11 with a view to obtaining a folded tube with a cross section that isoblong or of “B” form or, again, of any other form. It is then possibleto secure the assembly in the course of brazing the heat exchanger 1.

In a variant, the folding-over of the strip of material 11 at at leastan intermediate part 11 b to form one or more folds 13 may take placeprior to or after electrowelding to form the tube 5.

It will thus be understood that with the one or more fold(s) 13 formedat least at the nose of the tube 5 according to any of the embodimentsdescribed previously sufficient material is guaranteed at strategiclocations in such a manner as to withstand stresses, notably exteriorstresses, stressing the tube 5.

Naturally, other arrangements of the tube 5 that make it possible towithstand interior stresses, notably from the fluid, may be combinedwith these different embodiments described previously.

Such tubes 5 may be provided in any type of heat exchanger 1, notably abrazed heat exchanger, such as an engine-cooling radiator or, again, alow-temperature radiator or a condenser in an air-conditioning circuit.

The invention may likewise be applied to a front face or front facemodule incorporating one or more heat exchangers comprising such tubes5.

1. A tube for a heat exchanger made from a strip of material, the stripof material having two end parts joined such as to form the tube, thestrip of material forming the tube is folded on itself such as to defineat least one fold formed by two strip portions with continuity ofmaterial such that at least one strip portion of the fold: is a stripportion for protecting the tube in the event of an impact from anelement outside the tube, and is formed in an intermediate part of thestrip of material.
 2. The tube as claimed in claim 1, wherein theintermediate part lacks a join zone between the two end parts to closethe tube in a sealed manner.
 3. The tube as claimed in claim 1, whereinsaid at least one fold is formed along at least one lateral side of thetube.
 4. The tube as claimed in claim 1, wherein the strip of materialis folded such as to form a protuberance extending from the tube towardthe exterior of the tube.
 5. The tube as claimed in claim 4, wherein theprotuberance has a thickness at least equal to twice the materialthickness of the strip of material.
 6. The tube as claimed claim 4,wherein the protuberance forms, with the general plane of extension ofthe tube, a non-zero angle of the order of 30°.
 7. The tube as claimedin claim 4, in which the protuberance extends over a width equal to atleast twice and to at most ten times the material thickness of the stripof material.
 8. The tube as claimed in claim 1, wherein the strip ofmaterial is folded in the direction of the height of the tube, such asto form an excess thickness of material.
 9. The tube as claimed in claim8, wherein the height of the strip portions of said at least one fold isof the order of the height of the tube.
 10. A heat exchanger for a motorvehicle, comprising: a bundle of tubes, each tube of the bundle of tubesbeing made from a strip of material, the strip of material having twoend parts joined such as to form each tube, wherein the strip ofmaterial forming each tube is folded on itself such as to define atleast one fold formed by two strip portions with continuity of materialsuch that at least one strip portion of the fold: is a strip portion forprotecting each tube in the event of an impact from an element outsideeach tube, and is formed in an intermediate part of the strip ofmaterial.
 11. A tube for a heat exchanger made from a strip of material,the strip of material comprising two end parts joined such as to formthe tube, the tube comprising two lateral ends and an intermediate part;wherein the strip of material forming the tube is folded on itself suchas to define at least one fold formed by two strip portions withcontinuity of material such that at least one strip portion of the fold:is a strip portion for protecting the tube in the event of an impactfrom an element outside the tube, and is formed in the intermediate partof the strip of material, wherein the intermediate part is the portionof the tube that does not include the lateral ends of the tube and is alongitudinal extension corresponding to the longitudinal extension ofthe tube.